There are numerous references which describe latex paint compositions incorporating a vinyl acetate-ethylene emulsion as a binder. Representative patents include U.S. Pat. Nos. 3,404,112 and 3,404,113. The '112 patent discloses the use of vinyl acetate-ethylene latexes as a film-forming binder in an aqueous paint composition. The '113 patent incorporates a triallylcyanurate in the polymerization process to enhance the degree of insolubles. The particle size of the binder will range from about 0.1 to 2 microns. The ethylene content will range generally from 5 to 40, preferably about 10-15% by weight of the polymer.
U.S. Pat. No. 3,440,199 to Lindemann et al. discloses aqueous paint compositions incorporating an inter polymer of vinyl acetate, ethylene and glycidyl acrylate. The addition of the glycidyl acrylate into the polymer system enhances adhesion to raw wood without the use of a primer coat.
U.S. Pat. No. 4,219,454 to Iacoviello, et al. discloses the use of a vinyl acetate copolymer emulsion for preparing semi-gloss and flat interior paint compositions. Vinyl acetate-ethylene emulsions were disclosed with preferred latexes having a particle size such that less than 5% of the particles had a size greater than 0.65 microns and less than 5% had a particle size of less than 0.33 microns. Emulsions were prepared by introducing the monomers of vinyl acetate, optionally with a small amount of butyl acrylate into a stabilizer system of water, hydroxyethyl cellulose and multiple nonionic surfactants. The Tg of the vinyl acetate ethylene polymer was approximately 22° C., preferred levels of ethylene from about 10 to 15% by weight.
U.S. Pat. No. 5,470,906 to Craun, et al. discloses an aqueous ambient dry paint coating incorporating an emulsion copolymerized addition polymer containing an oligomer selected from polyurethane or polyester having a Tg below about −20° C. and a number average molecular weight between 300 and 5,000. The coating is free of organic coalescing solvents. Vinyl acetate and butylacrylate (80/20) are disclosed as conventional polymeric binders for consumer based paints with the binder having an elevated Tg lowered temporarily through the use of a volatile coalescing solvent. Low molecular weight oligomers of urethanes and polyester urethane copolymers were used in place of conventional coalescing solvents to achieve desired properties without objectionable odor and VOCs.
U.S. Pat. No. 3,969,296 to Wassenburg, et al. discloses a process for producing a vinyl acetate emulsion having improved adhesion characteristics against usual wet-cleaning with a cloth, sponge, etc. The emulsion is prepared by copolymerizing a small amount of a glycidyl ester of an alpha-beta ethylenically unsaturated acid with vinyl acetate followed by neutralization with ammonia.
U.S. Pat. No. 3,563,944 to Bauer et al. discloses a colloid-free vinyl acetate emulsion suited for producing paint formulations having good scrub resistance, film forming properties, mechanical stability, etc. The copolymer consists of vinyl acetate and a lower alkyl acrylate, or an alkyl maleate. Enhanced stability is imparted by polymerizing a portion of the monomers in a colloid-free aqueous medium and then adding more monomer during the course of reaction and using a nonionic surfactant to stabilize the polymerization.
The need today for architectural coating materials free from volatile organic content (VOC) for both safety and health reasons is well documented.
Latex paint compositions have captured a significant portion of the indoor and outdoor paint market because they have significant advantages as compared with organic solvent based paints. Three of the most important advantages are: cleanup is easier with latex paints than with solvent based paints; there is substantially less air pollution associated with latex paints as opposed to solvent based paints; and fire hazards from paint thinners and other solvents needed with solvent based paints are eliminated using latex paints. On the other hand, the coating properties and storage stability of latex paints have been somewhat inferior to those of the solvent type, particularly in obtaining desired film thickness, durability and adhesion. This is especially so in more modestly priced latex products with higher PVC.
Although a significant reduction or elimination of volatile organic solvents is achieved through the use of latex products, the surfactants remaining after water evaporation, coupled with the relatively high molecular weight of the polymers, frequently prevent complete coalescence, which is needed for superior durability, for example, scrub resistance. Conventional vinyl acetate based latex vehicles often require coalescing solvents in order for the latex to be suitable for use in a paint formulation. Coalescing solvents are incorporated into the paint composition to externally and temporarily plasticize the latex polymer for a time sufficient to develop film formation. This provides volatile organics, which are undesirable. That is, coalescing solvents diffuse out of the film after film formation and thus contribute to the VOC level emitted to the environment. Paints formulated with standard vinyl-acrylic latex vehicles and no coalescing solvent generally do not pass the requirement of film formation at temperatures as low as 40° F. Such paints also display cracking upon drying and provide poor durability. One approach to attempt to overcome these deficiencies is to increase the acrylate level to lower the minimum film formation temperature of the latex. In particular, acrylate monomers that lower Tg are effective, such as butyl acrylate. Although the approach addresses the cracking and durability problems, paints prepared from these latexes are more costly and they also display dirt pickup, due to unacceptable tackiness after drying. Therefore, one goal is to prepare a latex which permits a low film formation temperature without causing the dried film to become tacky and to have sufficient hardness to retain good durability.
Alkylphenol ethoxylates (APEs) represent a class of nonionic surfactants which are used in latex products to improve adhesion and film forming, and in paint formulations to provide pigment wetting. These compounds are believed to break down in the environment to related compounds that are persistent in the environment and act as endocrine disruptors. Due in part to regulations in Europe, as well as recently adopted water quality criteria in the United States, there is a need to use APE-free polymer emulsion binders in preparation of APE-free paint formulations. The evolving environmental controls of APEs are reminiscent of the 1970s ban on lead compounds in paint, enacted to prevent serious health risks, especially to children.
Conventional polymeric binders used in latex paint formulations are typically emulsion polymers containing surfactants that are based on alkylphenol ethoxylates. Previously known emulsion polymeric binders that are free of alkylphenol ethoxylates have not been popular, because they do not provide the necessary adhesion, perform more poorly as emulsifiers, and provide poorer color acceptance.
While the art is replete with formulations for latex paints, existing products, especially low-emission products, do not exhibit preferred characteristics in terms of film forming, durability, adhesion, or stain resistance and often include undesirable components, such as alkylphenol ethoxylates.